The invention relates to a process for the preparation of ferrierite.
Ferrierite is a crystalline aluminosilicate zeolite, which is used, inter alia, as adsorbent and as catalyst or catalyst carrier. Methods for its preparation are disclosed, e.g., in Journal of Catalysts, Vol. 35, 256-272 (1974), U.S. Pat. Nos. 3,933,974 and 4,000,248. It is known that ferrierite can be prepared by maintaining an aqueous mixture containing one or more alkali metal compounds, one or more aluminum compounds and one or more silicon compounds in a given ratio at elevated temperature until the ferrierite has been formed and subsequently by separating the ferrierite crystals from the motor liquor. This procedure has three drawbacks, which are connected with the reaction temperature, with the purity and the molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the ferrierite. As regards the reaction temperature it has been found that this procedure requires temperatures higher than 300.degree. C. These high reaction temperatures involve the use of high pressures, which necessitates the use of expensive high-pressure equipment. As regards the molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the ferrierite it has been found that this procedure produces as a rule ferrierite with a molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio lower than 15. When the ferrierite is used for catalytic purposes, a ferrierite with a higher molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio is needed in view of the catalyst stability. In the above-mentioned procedure the purity of the ferrierite leaves also much to be desired. As a rule a solid product is obtained consisting of less than 80 %w ferrierite.
The applicants have done an inestigation concerning the preparation of ferrierite. In this investigation a procedure was found which means a considerable improvement in connection with each of the three above-mentioned drawbacks.